Apparatus, circuitry, signals, probes and methods for cleaning and/or processing with sound

Abstract

The invention utilizes multiple frequency ultrasound generators driving multiple frequency harmonic transducer arrays at sweeping frequencies into the megasonic range. Generator signals that increase cavitation efficiency and that have successive time periods with predominantly stable cavitation and predominantly transient cavitation further improve the performance of the cleaning, microbiological inactivation, sonochemistry or processing systems. Probes that monitor the ultrasound and feedback the information to the generator provide consistency of process.

What is claimed is: 
     
       1. A method for cleaning or processing an object in a liquid medium comprising the steps of:
 driving two or more first transducer arrays coupled to said liquid medium for a first time period, each of said first transducer arrays being driven at an associated drive frequency said above frequencies being different from each other, 
 driving one or more second transducer arrays coupled to said liquid medium for a second time period, said second time period being of different duration than said first time period, each of said second transducer arrays being driven at an associated drive frequency. 
 
     
     
       2. The method of  claim 1  wherein said first time period precedes said second time period. 
     
     
       3. The method of  claim 2  wherein said first and second time periods are contiguous. 
     
     
       4. The method of  claim 2  wherein said first and second time periods are non-contiguous. 
     
     
       5. The method of  claim 1  wherein said second time period precedes said first time period. 
     
     
       6. The method of  claim 5  wherein said first and second time periods are contiguous. 
     
     
       7. The method of  claim 5  wherein said first and second time periods are non-contiguous. 
     
     
       8. The method of  claim 1  wherein said drive frequency of at least one of said second transducer arrays is the same as the drive frequencies of one of said first transducer arrays. 
     
     
       9. The method of  claim 1  wherein said drive frequencies of said second transducer arrays are different from said drive frequencies of said first transducer arrays. 
     
     
       10. The method of  claim 1  wherein at least one of said first transducer arrays includes only a single transducer. 
     
     
       11. The method of  claim 1  wherein at least one of said first transducer arrays includes two or more transducers. 
     
     
       12. The method of  claim 1  wherein at least one of said second arrays includes only a single transducer. 
     
     
       13. The method of  claim 1 , wherein at least one of said second transducer arrays includes two or more transducers. 
     
     
       14. The method of  claim 10  wherein one of said transducers of said first transducer array is one of said transducers of said second transducer array. 
     
     
       15. The method of  claim 11  wherein one of said transducers of said first transducer array is one of said transducers of said second transducer array. 
     
     
       16. The method of  claim 12  wherein one of said transducers of said first transducer array is one of said transducers of said second transducer array. 
     
     
       17. The method of  claim 13  wherein one of said transducers of said first transducer array is one of said transducers of said second transducer array. 
     
     
       18. The method of  claim 1  wherein said associated drive frequencies are ultrasound frequencies in the range between 18 Khz to 5 Mhz. 
     
     
       19. The method of  claim 1  comprising the further steps of:
 providing as a transducer of one of said first transducer arrays and said second transducer arrays, a transducer assembly extending along the transducer axis of said transducer assembly including:
 vi. a piezoelectric assembly including a stack of p polarized piezoelectric ceramic elements extending along said transducer axis between a piezoelectric assembly top surface and a piezoelectric assembly bottom surface, each of said polarized piezoelectric ceramic elements having an element top surface and an element bottom surface, and being characterized by a thickness Pi along said transducer axis, where i is an integer 1, 2, . . . , p, each of said element top surfaces and said element bottom surfaces having an electrically conductive layer disposed thereon, and including means for coupling a drive signal to said electrically conductive layers, 
 vii. a tank wall extending between a tank wall top surface and a tank wall bottom surface, said tank wall having a thickness T in the direction of said transducer axis, said thickness T being small relative to other thicknesses in said transducer assembly, said tank wall top surface forming said drive surface, and said tank wall bottom surface bonded to a front mass effectively adding a thickness T/2 to said front mass; 
 viii. said front mass extending between said tank wall bottom surface and said piezoelectric assembly top surface, said front mass having a thickness D in the direction of said transducer axis; 
 ix. a back mass extending between a bottom transducer surface and said bottom piezoelectric assembly surface, said back mass having a thickness B in the direction of said transducer axis; 
 x. a compression assembly including means for applying a compressive force F across said front mass and said back mass; 
 
 whereby said front mass, said piezoelectric assembly, said back mass and said tank wall are dimensioned so that in response to said compressive force F:
 P i  is equal to n i λ p /2 
 D+T/2 is equal to m 1 λ D /2+λ D /4 
 B is equal to m 2 λ B /2+λ B /4 
 
 where n i , m 1  and m 2  are integers and λ p  is the characteristic acoustic wavelength of said polarized piezoelectric ceramic elements, and λ B  and λ D , are the characteristic acoustic wavelengths of said back mass and said front mass, respectively [where λ=v/f] 
 wherein said transducer is characterized by a vibratory fundamental first frequency having wavelength λ f1  equal to 2 (Σ i P i +D+T/2+B) and a vibratory second frequency having wavelength λ f2  equal to 2λ P , and 
 coupling a drive surface of said transducer assembly to said liquid medium. 
 
     
     
       20. The method of  claim 1  comprising the further steps of:
 providing as a transducer of one of said first transducer arrays and said second transducer arrays a transducer assembly for operation at a first frequency within a megasonic range and at sweeping frequencies within a set of bandwidths which are within the frequency spectrum lower than said first frequency, comprising:
 a front mass with a front surface and a back surface; 
 a bonded structure consisting of a radiating diaphragm and a bonding material, said radiating diaphragm having a front surface and a back surface with said bonding material adhering said back surface of said radiating diaphragm to said front surface of said front mass; 
 a first polarized piezoelectric ceramic element with a front surface and a back surface, with said front surface of said first polarized piezoelectric ceramic element positioned adjacent to said front mass at said back surface of said front mass and forming a first interface there between; 
 a second polarized piezoelectric ceramic element with a front surface and a back surface, with said front surface of said second polarized piezoelectric ceramic element positioned adjacent to said first polarized piezoelectric ceramic element at said back surface of said first polarized piezoelectric ceramic element and forming a second interface there between; 
 a back mass with a front surface and a back surface, with said front surface of said back mass positioned adjacent to said second polarized piezoelectric ceramic element at said back surface of said second polarized piezoelectric ceramic element, forming a third interface there between; and 
 a clamping assembly for compressing said first polarized piezoelectric ceramic element and said second polarized piezoelectric ceramic element between said front mass and said back mass; 
 wherein said first polarized piezoelectric ceramic element and said second polarized piezoelectric ceramic element produce a resonant standing wave within said transducer assembly when driven by an electric signal at said first frequency; 
 wherein said front mass, said first polarized piezoelectric ceramic element, said second polarized piezoelectric ceramic element, and said back mass are each of a thickness such that when said transducer assembly is operated at said first frequency within said megasonic range, a first node of said resonant standing wave within said transducer assembly is positioned at said first interface, a second node of said resonant standing wave is positioned at said second interface, a third node of said resonant standing wave is positioned at said third interface, a first antinode of said resonant standing wave is positioned near said front surface of said front mass and within said bonded structure, and a second antinode of said resonant standing wave is positioned at said back surface of said back mass, and 
 coupling a drive surface of said transducer assembly to said liquid medium. 
 
 
     
     
       21. The method of  claim 1  comprising the further steps of:
 providing as a transducer of one of said first transducer arrays and said second transducer arrays, a Langevin structure bonded transducer assembly for producing a sound wave at a high frequency within the megasonic range comprised of:
 a front mass having a bonded front surface and a back surface and of a thickness equal to an integer number of half wavelengths plus one quarter wavelength of a high frequency resonant standing wave within said megasonic range such that an antinode of said high frequency resonant standing wave exists at said bonded front surface and a node of said high frequency resonant standing wave exists at said back surface; 
 a plurality of polarized piezoelectric ceramic elements arranged in a stack said stack having a front surface and a back surface, said front surface of said stack positioned adjacent to said front mass at said back surface of said front mass, at least one interface between each of said plurality of polarized piezoelectric ceramic elements within said stack, each of said plurality of polarized piezoelectric ceramic elements of said stack of a thickness equal to an integer number of half wavelengths of said high frequency resonant standing wave within said megasonic range such that a node of said high frequency resonant standing wave within said megasonic range exists at each of said at least one interface within said stack; 
 a back mass with a front surface and a back surface, the said front surface of said back mass positioned adjacent to said back surface of said stack and of a thickness equal to an integer number of half wavelengths plus one quarter wavelength of said high frequency resonant standing wave within said megasonic range such that an antinode of said high frequency resonant standing wave exists at said back surface of said back mass and a node of said high frequency resonant standing wave exists at said front surface; and 
 a clamping assembly for compressing said plurality of polarized piezoelectric ceramic elements of said stack between said front mass and said back mass, and 
 coupling a drive surface of said transducer assembly to said liquid medium.